Changing the Firefox Download Button
A couple months back we started a discussion around our plans for performing some multivariate optimization tests within the mozilla.com site. We started with one simple A/B test on a single web page and we now have some findings to share. At the Firefox customize page — www.mozilla.com/firefox/customize/ — we made a singular text change: the green download button could either include our default text “Download Now – Free” or our test text “Try Firefox 3″.

The results from the test are below. Please keep in mind that the primary purpose of this initial test was to evaluate a possible long-term solution/tool for implementing much more robust tests in the future. That said, our findings provide a small amount of insight. During the course of two weeks, this page saw about 300K visitors and nearly 30K clicks to download Firefox. The conversion rate for “Download Now – Free” was 10.07% versus 9.73% for “Try Firefox 3″, which translates to a 3.44% decrease in optimization when using “Try Firefox 3″, with 99.85% confidence in these results (confidence = likelihood that this version of the page performs significantly different than our default page).
If we’ve piqued your interest, please note that we’ll soon have some exciting findings related to a currently ongoing multivariate test at the main Firefox product page (www.mozilla.com/firefox).

“Try …” is wording I usually see for shareware and demos, not for full versions.
I’d suggest that the lower conversion rate is for two reasons:
1) It is not as obvious what will happen when you click ‘Try Firefox’
2) It makes it sound more like you are downloading a time/feature-limited demo version.
I would say “Download now- Free” is better since it has a call to action and also lets the user that Firefox is free (in case the user does not know, which is probable in the case of novice internet users)
Try Firefox 3 doesn’t let the user know whether it is free or not and as Minh suggests, is what would be appropriate for shareware and demo software.